This invention relates to safety devices for hydraulic systems. More specifically, the invention relates to a hydraulic velocity fuse safety device operable to selectively protect systems which may function at any of several selected fluid flow rate settings.
Heretofore hydraulic fuses have been used, for example, in aircraft systems to prevent the escape of hydraulic fluid in the event of a rupture somewhere in the closed hydraulic system. Such fuses are configured so that the fluid flow passage is closed when a selected rate of fluid flow in the line is exceeded. Such existing devices are useful in systems which operate only at one selected rate of flow of hydraulic fluid.
Hydraulic systems typically in use, such as those used on mobile truck mounted systems, however, suffer from the lack of appropriate protective devices. Thus, in the event a hydraulic hoist is used, a 25 to 50 gallons per minute of hydraulic fluid flow is required. Subsequently, after a worker has been elevated to a selected height, a portable tool operated by the same hydraulic system may be needed. Such a tool, however, may require a hydraulic fluid flow rate of only five to ten gallons per minute. On many jobs it is necessary to work, alternately, with tools requiring different fluid flow rates. It has been impractical to protect such systems with prior art hydraulic fuses, particularly in view of the fact that the hydraulic fluid flow rate varies greatly when the engine rpm's on host vehicle are increased. Thus, a 10 gpm fuse would not protect workers using a 50 gpm tool.
Often, when a hydraulic hose ruptures, the hot hydraulic fluid in the system escapes in the form of a hot oil spray. This escaping hot hydraulic fluid may severely burn the affected workers and also may be sprayed into the surrounding area with resultant environmental damage. A great need has thus existed for improved safety devices for such hydraulic systems.